Selective signaling system



Sept. 4, 1928. 1,683,127

T. M L. DAVIS SELECTIVE SIGNALING SYSTEM Filed May 12, 1926 I? 1 T; E

INVEN TOR. 72077743 /%Z fia m's,

flll W A TTORNEY Patented Sept. 4, 15928.

UNITED STATES PATENT OFFECEQ THOMAS MEL. DAVIS, OF WASHING-TON, DISTRICT OF COLUMBIA, ASSIGNOR TO WIRED RADIO, INCL, OF NEW YORK, N. Y

., A CORPORATION O13 DELAWARE.

SELECTIVE SIGNALING SYSTEM.

Application filed May 12, 1926. Serial No. 108,666.

My invention relates broadly to alternating current circuits and more particularly to an electrical tuning system for radio frequencies whereby by accurate adjustment of the tuning circuits it is possible to accept a desired frequency, to the exclusion of undesired frequencies.

One of the objects of my invention is to provide a radio frequency trap circuit for signal receiving systems for excluding interfering frequencies from the signal receiving circuit while being efficiently responsive to a selected frequency.

Anotherobject of myinvention is to provide an arrangement of frequency selective circuits which may be readily adapted for connection in a variety of alternating current systems for obtaining a high degree of selectivity.

Another object of my invention is to provide a double trap circuit for signal receiv ing systems having a plurality of branches which may be selectively connected in the receiving circuit for securing efficient response to signals of a given frequency while exeluding from the receiving circuit signals of interfering frequencies Another object ofv my invention is to proide a double trap circuit for signal receiving systems in which a plurality of branches are provided for establishing two series cir cuits through the two traps to the signal receiving system where one of the traps'may be tuned to resonance with the interfering signal for the exclusion thereof while the second trap may be adjusted sot-hat its capacitive reactance will be equaland opposite to the inductive reactance of first or excluding unit for securing selective reception of incoming signaling energy.

Still another objectof my invention is to provide a combination of trap circuits for signal rei'ieiving systeuls wherein a pair of independent series paths for the incoming signals maybe provided through inductive or capacity elements which are disposed in parallel. relationship, with means for independently shunting the parallel connected elements for adjusting one trap unitfor the exclusion of the undesired frequency.

A still further object of my invention is to provide an interference prevention unit for signal receiving circuits wherein two inclependent traps are employed. witl'i means for separately tuning each of the trap units for establishing two series resonant circuits through the traps, each of the traps being parallel connected devices which may be adjusted for the exclusion of undesired frequencies, while permitting selective reception of a desired frequency. i i

A parallel tuned circuit when placed in a radio circuit such as an antenna, will act as a trap to the frequency to which it is tuned by virtue of its high series impedance. The effect of such a unit is not confined to the resonant frequency but is more or less effective over a band the width of which depends upon the inherent losses of such a combination while the degree of maximum ex breadth does exist, even in the lowest loss trap units practicable to'build, I have devised various forms of double trap units which to a great degree reduce this effective breadthymaking it possible to receive signals very close to the trapped frequency v and much closer than it has heretofore been possible.

My invention will be more clearly understood by referring to the accompanying drawings in which: t

Figure 1 illustrates one arrangement of the double trap circuit of my invention connected in a radio receiving system; Fig. 2 illustrates a modified arrangement of the double trap circuitfor signal receiving circuits; Fig. 3 shows still another modification of the doubletrap circuit of my invention; and Fig. 4; illustrates the application of the double trap circuit of my invention to wired radio receiving systems.

I have illustrated the traps schematically in the drawings as applied to an aperiodic antenna circuit and to a wired radio system which feeds a receiv r thru an inductive coupling. In Fig. 1 of the drawings two traps 9 and 10 are shown in an antenna ground circuit 12. The signal receiving circuit is represented as coupled to the antenna ground s stem 1-2 through coupling transformer 3 having primary winding 4:

lUli

which extends through coupling transformer 8 to-the remainder of the receiving apparatus.

Each trap 9-and 10 employsa variable condenser 11 and 14 with fixed or stepvariable inductance systems 12 and 15. With this arrangement it is possible to tune one trap to exclude an interfering signal While the other trap is shorted out by virtue of switches 16 or 17, then by cutting in the second trap by means of switches 1 6 and 17 it may be tuned to improve theintensity of the signal which is desired for reception.

. This improvement is most effective when the two signals are comparatively close togctlier and it is in this ran e that the double trap unit ismost valuab e. By reference to Fig. 1, it will be noted that when both traps 9 and 10 are in the circuit, there are two paralleltraps in series with the antenna 1 and there are two series. circuits thru the two traps from the antenna 1 to the receiver. Either of n the parallel circuits may be tuned to'resonance with the inter:

' fering signal for exclusion While the second trap condenser 14 can be tfuned so that its capacitive reactance will beequal and oppo-= combination is practically independent" of effectfrom antenna capacity variation. The double trap unit has the added advantageof giving double exclusionto a strong interference tuning them both to resonance.

In Fig. 2 av combinationof two traps 9 and 10' which possess all of the features hereinbefore mentioned are I provided, but

7 lII addition, have a variometer18 in one unit instead of a fixed inductance thereby making it possible to obtain two series resis set for exclusion.

onant circuits thru the traps when trap 10 i In Fig. 3 two traps 9 and 10 are shown in which both inductances 18 and 19 are variable which gives additional flexibility "permitting the use of either unit as the exclusion trap with the ability I to obtain series resonance thru either or both. of the legs bv tuning theother trap inductance'and capacity elements separately to. series signal resonance. a n a In Fig. 4 lhave, shown the double trap system 9-10 of my invention applied to a wired radio receiving circuit wherea desired carrier frequency may be, received to the exclusion of other carrier frequencies The combination of the twoparallel tuned traps, which have means for independently Y i'enderingthe tuning elements thereof efiiec tive or ineffective, operates to exclude nndesired frequencies from the. signal receiving circuit while permitting selective. reception of a desired frequency.

lV-hile l have shown several different embodiments of the doubletra-p circuit, I desire thatit be understood that even further. modifications may be 1 made and that no liniitationsupon my invention are ntended .other than are imposedby'the'scopeof the appended claims. -For example, I- may readily emplo the principles of my invention in the elimination of harmonic frequencies in transmitted circuits.- A variety of applications of my invention will readily suggestthemselves to those skilled in the art. y a

'Whatfl claim as new and desire to secure by Letters Patent of the United States is as 1. interference prevention circuit for signal receiving systems compris ng in combination with. a. signal receiving circuit a pair of trap circuits, each of said trap circuits lcomprisingwariable inductance and capacity" connected in parallel, with one of said trap circuits series connected with the other of said trap circuits and means farindependently shunting either of saidtrap circuits,the inductanceand capacity in one Of said trap, circuits being arranged to be tuned to resonance with an interfering fre uency for the exclusion thereof,"while the ot er of saidtrap circuits may haveits capacitive reactancead'justed to a. value equal and oppo site to the inductive reactance of the other.

trap circuit.

2. An interference prevention circuit for signal receiving systems comprising in comhination with a signal receiving circuit, a pair of series connected trap cir'cuitseach consisting of tunable elements connected in parallel a tunable element ofone ofsaid trap"circuits providing With a tunable element :of the other oflsaid trap circuits at series path to said signal 'eceiving circuit, whereby two series circuits are provided through said trap circuits tofsaid signal re-.

ceiving circuit, and means f or rendering the elements in a'selected one of saidtrap circuits effective brinefl'ective for the selective reception of a predetermined frequency to the exclusion of other frequencies. n

' 3. A signal receiving system comprising in combination with aesignal receiving cir-.

cuit,- a pair of trap circuits each having parallel connected tunable elements, with the tunable elements of one trap series connected with the tunable elements of the other trap and disposed in series. with said signal re ceivingeircuitiseparate tunable elements in each of saidtrap circuitsafi'ording a series path of substantially zero reactance and other tunable elements in each of said trap circuits, aflording an independent series path approaching substantiallyzero reactance to the desired signal frequency whereby one of the traps excludes undesired frequencies and the other of said traps operates to further exclude undesired frequencies for the selective reception of a desired frequency.

4. In a signal receiving system an interference prevention circuit connected in series with the receiving system, said interference prevention circuit comprising separate parallel connected systems, each .including'capacitive and inductive reactances, one of said parallel connected systems being arranged to be tuned to resonance with the interfering frequency for the exclusion thereof from said signal receiving circuits, While the other said parallel connected system has its capacitive reactance adjustable to a value equal and opposite to the inductive reactance of the first mentioned parallel connected systern for excluding undesired frequencies and selectively receiving desired frequencies.

THOMAS MoL. DAVIS. 

